Among a number of switching devices, the diffuse gas discharge switch has proved to be a promising one for a system such as inductive energy storage in which repetitive and rapid switching is required. In particular, the use of an external electron beam or laser to sustain a volume gas discharge in the switch is advantageous because excessive heating of the electrodes and the gas can be avoided, and the discharge can return to its initial state of high resistivity very quickly once the source of ionization is removed.
The operation of a diffuse discharge switch used for inductive storage is characterized by two distinct stages. The first is a conducting or storing stage where the field in the switch is small. It is desirable in the conducting stage for the electron current density to be high by maximizing the electron drift velocity and simultaneously minimizing the average energy that is required to produce an electron-positive ion pair. When the electron drift velocity is maximized, more current is flowing through the switch and, therefore, more power is being stored in the inductor. When the energy required to produce an electron-positive ion pair is minimized, more electrons will be formed for a given amount of energy expended. Both these factors contribute to the free flow of electrons through the switch.
The second stage is the transferring stage when the stored energy in the inductor is transferred in a pulse to the load. During this stage, opposite characteristics of the gas within the switch are required than of the first stage. The dielectric strength must be large so that the gas can readily withstand the high induced voltage without breakdown. This can be done by the formation of negative ions by attachment of electrons to gas molecules.
The electron drift velocity is affected by the type of gas that is present in the switch. Since it is desirable to have a high electron drift velocity during the conducting stage and a low electron drift velocity during the opening stage, the gas in the switch must be able to perform two opposite functions. To achieve this, gas mixtures have been developed that have both good electron conducting properties and electron attaching or insulating properties so that the benefits of each during the respective stages can be realized. Previous development of such gas mixtures by the applicants is set forth in U.S. Pat. No. 4,490,650 issued Dec. 25, 1984. Although the gas mixtures previously developed can carry a significant amount of energy in order to achieve a strong pulse with great power, it is necessary to extend the capability of the switch to carry more current with a resulting increase in the amount of the energy that can be stored in the inductor. Existing gas mixtures have limits on their conducting capabilities when the switch is closed; therefore, there is a need to develop a gas for the diffused discharge gas switch that allows high current flow but has sufficient insulating capabilities to withstand an increase in the voltage when the current source is discontinued.